1. Field of the Invention
The present invention relates to a filter assembly, and more particularly, to a low hold-up volume filter assembly which provides for reduced fluid hold-up volume waste when replacing filters and for even flow distribution through the filter during normal operation.
2. Discussion of the Prior Art
A potentially costly problem associated with the use of any filter assembly is the problem of hold-up volume waste. When a filter element must be replaced, typically during routine maintenance, a portion of the fluid remains within the filter element housing. The remaining fluid generally cannot be reused due to possible contamination; therefore, this excess fluid must be disposed of, and depending upon the fluid, the replacement of the fluid can be costly. For example, in the integrated circuit industry, photo lithography is a technique utilized in various mask work procedures. Photoresist is a light sensitive chemical mixture which is used in photo lithography. In the photo lithography procedure, the photoresist is pumped onto a spinning disc which spreads the viscous photoresist over the particular work product. The pump assembly utilized has a filter housing that accepts a small disposable filter which must be replaced periodically and excess photoresist in the filter housing is lost. A typical positive photoresist can cost up to six hundred dollars or more per gallon, making waste extremely costly. In addition to the direct cost of replacing the wasted fluid, there is the cost of disposal. There are environmental factors which need to be considered in the disposal of certain chemicals thereby making disposal as potentially costly as buying new chemicals.
Another typical problem encountered in filter use is the problem of uneven fluid flow. For example, where more fluid flows through the upper portion of a filter element than through the lower portion, more dirt and/or other debris is deposited on the upper portion of the filter element than on the lower portion. This uneven loading of the filter element can shorten the life of the filter element, which results in more frequent replacement of the filter element and increased material and labor costs, as well as longer system down time.